Summary A de Havilland DHC-2 Beaver floatplane, C-GVHT (serial number 257), took off from Campbell River, British Columbia, at 1530 Pacific daylight time, with a pilot and four passengers on board. The aircraft was on a visual flight rules flight to a logging camp on Mackenzie Sound, 76 nautical miles northwest of Campbell River, and was scheduled to arrive at 1700. When the aircraft arrived over the Mackenzie logging camp, the pilot informed ground personnel by radio that he was overhead at 2800 feet, between cloud layers with no place to descend, and that because of unfavourable weather conditions, he was returning, presumably to Campbell River. The aircraft then flew to a clear area north of the camp and entered the Frederic Creek valley. When company ground personnel could not contact the aircraft by radio, they began a ground search, later followed by an aerial search. The searches were hampered by poor weather. The aircraft wreckage was found three days later, about four nautical miles northeast of the camp. The accident occurred at 1706 in daylight conditions. All occupants were fatally injured, and the aircraft was destroyed. The emergency locator transmitter was destroyed on impact and did not transmit a signal. No fire occurred. Ce rapport est galement disponible en franais. Other Factual Information The aircraft was owned and operated by Wahkash Contracting Ltd. based in Campbell River, British Columbia, and was normally used to ferry loggers to and from logging camps. The float-equipped aircraft operated only from water surfaces. After departing Campbell River water aerodrome in the afternoon on the day of the accident, the aircraft flew northwest for 43minutes before making a brief, intermediate stop at a company logging camp at Hoeya in Knight Inlet, 49 nautical miles from Campbell River. After a small consignment of food was offloaded, the aircraft departed Hoeya at 1629 Pacific daylight time1 and arrived overhead the Mackenzie camp 25minutes later. The aircraft then continued flying in the area for 12more minutes, until the accident. At the time, the ceiling over the camp, which is at sea level, was between 1600 and 1700feet. It was reported that the north end of the south Frederic Creek valley was free of cloud at the time of the accident but that cloud was moving through a pass into the valley at the south end. One of the managers of the camp, who was on a logging road in the south valley, advised the pilot to come to the Frederic Creek area because it was clear of cloud. The pilot then flew northeast to Wakeman Sound, where he advised that he could descend below the cloud to the Frederic Creek inlet. The aircraft flew west along Frederic Creek until turning left toward the pass in the south Frederic Creek valley. The pass crosses a north-south divide (saddle); the valley to the east of the divide turns south immediately and descends to Mackenzie Lake. (See Figure1.) The pilot was also advised that the ceiling in the pass was between 300 and 400feet above ground level and that about 1500feet would be needed to go through the pass. The pilot reported that he was unfamiliar with the area but that he would continue and assess the conditions. The aircraft flew south toward the pass and made one circuit of the valley. After the circuit, the aircraft again flew toward the pass, then executed a sharp left turn about 10seconds before the accident. The aircraft was flying away from the pass at impact. The last brief radio transmission from the pilot was at 1706, only seconds before impact. During the second attempt, the turn radius was smaller and the ground speed slower than in the first circuit, allowing the aircraft to come closer to the pass. As a result, the aircraft was forced to turn in a more confined area. During a level turn, as the angle of bank increases, the stall speed also increases. Table1 summarizes aircraft stall speeds contained in the Transport Canada - approved DHC-2 Beaver flight manual (PSM 1-2-1). No stall speed information was found for other flap settings. In part, the flight manual warns that, in tight turns, flight load factors may also increase the danger of an unintentional stall. The flight manual advises that it is possible to retain full control of the aircraft at 65 mph with the flaps in the landing position. Flight path data shows that the accident Beaver's ground speed was approximately 70mph just before the loss of control. The wreckage was found on the east side of the south Frederic Creek valley, about 0.3nautical mile from the pass near the south end of the valley. The wreckage was found inverted and heading south, at the base of two large trees at the 1100-foot level in a heavily treed area. Most of the damage to the trees at the accident site occurred to the northern exposures of two large trees, which were 25feet apart and about 120feet tall. These trees had scrape marks and wing-paint transfer down the lower 60feet of the trunks. None of the trees in the area surrounding the wreckage had any recent broken branches or broken treetops. Although the aircraft was extensively damaged, all aircraft components and flight control surfaces were found at the accident site. All seats had broken away from their mounting points on the cabin floor. The emergency locator transmitter had detached from the bracket on the inside wall of the fuselage. The left control wheel of the dual control column had both horns broken off; the right control wheel remained intact. The forward fuel tank had ruptured at impact and was found empty; the inside of the cabin beneath the tank smelled strongly of fuel. A significant amount of clean blue fuel was found in the centre and aft tanks. A cargo net was found stowed in its bag in the cabin - it had not been used to secure 300 pounds of cargo, nor was any other means of securing the cargo found. The cargo had moved forward into the area of the cabin. Damage to the aircraft is consistent with high deceleration forces and an inverted attitude at impact; such forces exceed human tolerance. The accident was not survivable. C-GVHT was equipped with EDO 4930 floats and was manufactured in 1951; total airframe time at the time of the accident was approximately 11325hours. The most recent mechanical inspection was completed at 11207hours on 27June2001, 47 days before the accident. Logbooks and maintenance records indicate that the aircraft had been certificated, equipped, and maintained in accordance with existing regulations and approved procedures. In March1998, a cabin extension kit (supplemental type approval SA90-2, configuration 3) was installed on the aircraft. This kit included the installation of an Alaska cargo door, which significantly increased the volume of the original Beaver baggage compartment. Installation of the larger cargo door made it easier to load bulky cargo into the baggage compartment and changed the moment arm of the cargo compartment from 94 to 97inches aft of the datum. The floor loading limit remained unchanged. No indication of any pre-existing airframe defect, engine malfunction, or system deficiency was found. The propeller blades exhibited damage consistent with an engine delivering power at impact. Continuity of the flight controls was established. The flap actuating cylinder was found extended to a position that corresponds to the 35 setting, which is the take-off position. This flap position is often used in slow flight. Flight in accordance with visual flight rules (VFR) require pilots to maintain visual reference to the surface and remain clear of cloud.2 VFR flight above cloud (VFR over-the-top) is permitted, provided that certain conditions are met in accordance with Canadian Aviation Regulations (CARs), including weather minima, aircraft equipment, and pilot qualifications.3 The pilot held a valid Canadian private pilot licence - aeroplane, issued by Transport Canada (TC). The pilot did not hold an instrument rating or a VFR over-the-top rating. Records show that as of August2000, he had accumulated more than 4000 hours' total flying time. The aircraft journey log indicated that his first flight to the Mackenzie logging camp was on 01June2001, 73 days before the accident, and that he had flown there 21times since. It was reported that the pilot had flown above the cloud on an earlier flight on the day of the accident. The maximum certificated all-up weight (MAUW) of the DHC-2 Beaver on floats is 5090pounds, with an aft centre of gravity (CG) limit of 6.1inches aft of the datum. In comparison, the MAUW of the Beaver on wheels is 5100pounds, but the aft CG limit is 8.8inches aft of the datum. TC records show that C-GVHT was last weighed on 13March 1998, at which time the aircraft empty weight was calculated to have been 3550pounds, with a CG of 2.41inches forward of the datum. The aircraft was previously weighed on 20August1988, at which time the aircraft empty weight was calculated to have been 3275pounds, with a CG of 0.31inch aft of the datum. This calculation had been based on a previous weight and balance revision, dated July 1986, which showed that the aircraft was 3317pounds, with a CG of 0.9inch forward of the datum. A TSB review of this calculation reveals that the CG figure is erroneous and is 1.8inches too far forward - that is, it should have been 0.9inch aft of the datum. The current aircraft journey log recorded the empty weight as 3275pounds - that is, 275pounds underweight. This figure was apparently used by the pilot. It is unknown which CG the pilot used. To provide pilots with accurate weight and balance information for their aircraft, CARs require that the most recent weight and balance document be kept on board an aircraft. A weight and balance document for C-GVHT was found with the aircraft journey log on board. However, the document had been prepared in July1986 and showed an empty weight of 3317pounds, with a CG of 0.09inch forward of the datum. A TSB review of this calculation reveals that the CG figure is erroneous and is 1inch too far forward. (Note: This CG figure differs from the one used in the revision of August1988 mentioned previously.) Furthermore, a plastic-laminated load sheet, dated 18June1978, that was used by pilots to quickly calculate acceptable aircraft loading, was also kept with the aircraft journey log and showed an aircraft empty weight of 3388pounds, but without a CG figure. Section RAC 3-2 of TC's Aeronautical Information Publication(AIP) (TP2300) advises that actual passenger weights should be used to determine the weight and balance of an aircraft, but in the event that individual weights are not available, an average passenger weight may be used. AIP prescribes that the standard average weight for adult male passengers is 182pounds (summer) and 188pounds (winter).4 Figure2. Weight and balance calculations for C-GVHT The pilot loaded the aircraft at Campbell River himself, as was his practice. There is no information that the cargo or passengers were weighed before the flight. Weight and balance calculations by TSB, using actual weights of the occupants and cargo carried, show that, at take-off from Campbell River, the aircraft was 5364 pounds, with a CG of 8.7inches aft of the datum - 274pounds over MAUW and 2.6inches outside the aft CG limit. Calculations also showed that the aircraft was overloaded by approximately 59pounds at the time of the accident and that the CG was 1.6 inches outside the aft limit. (SeeFigure2. Note that this graph also shows the aft CG limit for the wheels configuration.) The DHC-2 Beaver has known stall characteristics when loaded at the aft CG limit. Since the accident aircraft was loaded over the maximum allowable weight and outside the aft CG limit, the stall characteristics were unproven. However, the following information gives valuable insight into the possibilities:5 The DHC-2 aircraft was designed and certified to meet British Civil Airworthiness Requirements, published in 1945. At that time, the British Air Registration Board's policy was that tests to prove compliance . . . need only be made at such points in each range as are necessary for reliable inferences to be made of the behaviour of the aeroplane over the remainder of that range. In part, the specific certification requirements regarding aircraft stall characteristics state that as the stall is approached from straight flight, there shall be no violent wing dropping and no tendency to spin and the aeroplane should give, by juddering or other means, clear warning of the approach to the stall from straight or turning flight. In the case of the DHC-2, the aircraft is not equipped with any aural or visual stall warning system, and warning of an impending stall is dependant on juddering or on some other aerodynamic indication. Washington-based Aeronautical Testing Service Inc. (ATS) is an aeronautical consulting and manufacturing company involved primarily in the engineering, development, and manufacture of modifications for general aviation aircraft. According to company literature, ATS was created to help increase the safety and performance of general aviation aircraft by designing and building vortex generator kits for use on a variety of general aviation and agricultural aircraft. ATS completed flight tests on an un-modified DHC-2 MKI aircraft as part of a vortex generator design for that aircraft type. These tests evaluated the stall characteristics, stall warning, and controllability of the stall in a variety of weight and balance configurations that were not specifically required by the original British Civil Airworthiness Requirements. The flight test report of that activity indicates that with a forward CG, the stall characteristics of the aircraft were acceptable. However, with an aft CG and with power on, departures of 60degrees of roll, 30 to 40degrees of yaw, and 30 degrees of pitch were reported as being common during these flight tests. With the flaps selected to the climb, take-off, and landing positions, the ATS flight test report indicates that the ailerons and rudder were effective up to the point of the stall but were not adequate to control the violent roll and yaw once the stall occurred. A positive elevator movement was required to recover from the stalled condition before the aircraft began to spin. Test pilots with the TC Flight Certification Branch and with de Havilland have not experienced such violent stall characteristics as described by both ATS and by the accident pilot involved. The TC Aircraft Certification Branch subsequently indicated that it will examine the DHC-2 service history and stall characteristics to determine whether any mandatory changes are warranted. On 24 January 2001 TC completed a review of some 200TSB and 89National Transportation Safety Board (NTSB) occurrence reports of Beaver incidents. There were 13TSB and 8NTSB occurrences that were suspected of being related to wing stalls. It was further determined that there were no other reports which clearly demonstrated a stall occurring at or above 80mph, as stated in report A98P0194. A stall warning device is not required on the DHC-2 Beaver as part of its certification, and review of its service history data indicates that aircraft safety has not been adversely affected so as to warrant mandatory corrective action.